Cold pressure welding has been used extensively to join non-ferrous metals for making electrical connections. Up to the present time, the use of cold welding to join metals has resulted in considerable deformation of the materials in the area of the weld joint. Consequently, the use of cold pressure welded joints in electrical transformer windings has resulted in significant loss of space, generally referred to as space factor, in the coils. In the design of a transformer coil, careful consideration is given to eliminating wasted space. Any space in the coil between conductor layers or layers of conductive turns not required for insulating, cooling or other electrical purposes increases the product's costs.
Conventional cold pressure welding makes use of one or more indentors which penetrate a sandwich of two or more materials to be joined causing a flow of metal that produces a metallurgical bonding of the materials. During penetration of the materials, the materials are forced against an anvil or base plate and in most cases held there by a stripper plate which has holes that allow the indentor to pass through to penetrate the materials. The stripper plate is commonly die spring loaded which generally can impart enough force so that the materials are held against the anvil during indentor removal. As the indentors penetrate the materials, the displaced metal flows away from an area in front of each indentor in a perpendicular direction from the penetration causing material in the area surrounding each indentor to expand. This expansion causes the length and width of the sandwiched materials to grow which causes buckling. At the same time indentor bulges occur due to the inability of the stripper plate to constrain the sandwich to a desired thickness. An example of such prior art cold pressure welding is illustrated in FIGS. 1 and 2. Other examples of prior art cold pressure welding are illustrated in U.S. Pat. Nos. 2,522,408 and 2,707,821.
It would be desirable to provide a method and apparatus for cold pressure welding wherein the distortion and buckling of the non-ferrous metal parts being cold welded or joined is substantially eliminated.